U.S. patent number 10,009,929 [Application Number 15/079,312] was granted by the patent office on 2018-06-26 for contention-based random access.
This patent grant is currently assigned to Sprint Spectrum L.P.. The grantee listed for this patent is Sprint Spectrum LP. Invention is credited to Muhammad Ahsan Naim, Luca Zappaterra, Yu Zhou.
United States Patent |
10,009,929 |
Zhou , et al. |
June 26, 2018 |
Contention-based random access
Abstract
Retransmission parameters are determined for a wireless device
based on a desired retransmission success rate, that is, a
probability that subsequent random access requests transmitted from
the wireless device re-initiating a contention-based random access
procedure with an access node will reach the access node. The
retransmission parameters are determined based on at least a
quality of service associated with the wireless device, a distance
of the wireless device from the access node, and a cell load of the
access node. The retransmission parameters include a retransmission
power and a retransmission backoff window size. A product of the
power and backoff window is scaled such that it can be equated with
a retransmission success rate.
Inventors: |
Zhou; Yu (Herndon, VA),
Naim; Muhammad Ahsan (Ashburn, VA), Zappaterra; Luca
(Arlington, VA) |
Applicant: |
Name |
City |
State |
Country |
Type |
Sprint Spectrum LP |
Overland Park |
KS |
US |
|
|
Assignee: |
Sprint Spectrum L.P. (Overland
Park, KS)
|
Family
ID: |
62598994 |
Appl.
No.: |
15/079,312 |
Filed: |
March 24, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04W
74/0833 (20130101); H04W 52/48 (20130101); H04L
1/1825 (20130101); H04L 47/27 (20130101); H04W
52/20 (20130101); H04L 1/0001 (20130101) |
Current International
Class: |
H04W
74/00 (20090101); H04W 74/08 (20090101); H04W
52/20 (20090101); H04L 12/807 (20130101); H04W
52/48 (20090101); H04L 1/00 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Wong; Warner
Claims
What is claimed is:
1. A method for random access in a wireless network, the method
comprising: determining a retransmission power and a backoff window
for a retransmission of a connection request to an access node from
at least one of two or more wireless devices; comparing a scaled
product of the retransmission power and backoff window with a
predefined retransmission success rate; determining that the scaled
product is lower than the predefined retransmission success rate;
and increasing one or both of the retransmission power and the
backoff window prior to transmitting the retransmission power and
backoff window to the at least one of said two or more wireless
devices.
2. The method of claim 1, wherein determining the retransmission
power and backoff window is triggered by a collision between
connection requests from the two or more wireless devices.
3. The method of claim 1, wherein the retransmission power and the
backoff window are subject to one or more maximum constraints based
on a cell load of the access node.
4. The method of claim 1, wherein the predefined retransmission
success rate is based on a quality of service (QoS) associated with
the at least one of said two or more wireless devices.
5. The method of claim 1, wherein determining the retransmission
power is based on a distance between the access node and the at
least one of the two or more wireless devices.
6. The method of claim 1, wherein determining the backoff window is
based on one or more of a cell load of the access node and a packet
delay budget based on a quality of service (QoS) associated with
the at least one of said two or more wireless devices.
7. The method of claim 6, further comprising determining the scaled
product using a scaling factor for the backoff window, the scaling
factor being based on the cell load.
8. The method of claim 1, further comprising: determining that the
scaled product is substantially higher than the predefined
transmission success rate, and decreasing one or both of the
retransmission power and the backoff window.
9. A system for random access in a wireless network, the system
comprising: an access node for providing network services to one or
more wireless devices; and a processor communicatively coupled to
the access node, the processor for configuring the access node to
perform operations comprising: obtaining a location and a quality
of service (QoS) of a wireless device that lost a contention-based
random access procedure; based on the location, the QoS, and a cell
load of the access node, determining a retransmission power and a
backoff parameter for the wireless device, wherein a scaled product
of the retransmission power and the backoff parameter represents a
success rate for a subsequent preamble transmitted by the wireless
device; determining that the scaled product is lower than a
threshold success rate; increasing one or both of the
retransmission power and the backoff window until the scaled
product meets the threshold success rate; and upon determining that
the scaled product meets the threshold success rate, transmitting
the retransmission power and the backoff parameter to the wireless
device.
10. The system of claim 9, wherein the operations further comprise
determining the threshold success rate based on the QoS.
11. The system of claim 9, wherein the cell load comprises a cell
load of a physical random access channel (PRACH) of the access
node.
12. The system of claim 11, wherein the operations further comprise
determining a maximum retransmission power based on the cell
load.
13. The system of claim 9, wherein the operations further comprise
transmitting the retransmission power to the wireless device via a
system information block (SIB) message.
14. The system of claim 9, wherein the operations further comprise
transmitting the backoff parameter to the wireless device via a
backoff indicator message.
15. A processing node for random access in a wireless network, the
processing node comprising a processor for enabling the processing
node to perform operations comprising: determining a retransmission
power and a backoff window for a preamble transmitted by a wireless
device to an access node; scaling the backoff window based on a
cell load of the access node; comparing a product of the
retransmission power and the scaled backoff window with a
predefined threshold; determining that the product is lower than
the predefined threshold; and increasing one or both of the
retransmission power and the backoff window, wherein the predefined
threshold represents a probability of success of the preamble
reaching the access node.
16. The processing node of claim 15, wherein the operations further
comprise determining that the product is higher than the predefined
threshold, and decreasing one or both of the retransmission power
and the backoff window.
17. The processing node of claim 15, wherein the increasing is
performed subject to one or more constraints based on the cell load
of the access node.
Description
TECHNICAL BACKGROUND
A wireless device attempting to establish communication with a
wireless communication network typically sends a request for a
communication channel to an access node using a random access
procedure. There are two types of random access procedures:
contention-free and contention-based. A contention-free random
access procedure is used when, for example, a wireless device is
handed over from one access node to another access node. A
contention-based random access procedure is used when, for example,
a wireless device exits an idle mode and attempts to re-establish
communication with an access node, a wireless device temporarily
loses communication with an access node and attempts to
re-establish communication, data is available to be transmitted
from the wireless device to the access node, etc. In a
contention-based random access procedure, a wireless device
typically sends a channel request over a randomly selected random
access channel (RACH) or physical random access channel (PRACH).
The channel request can comprise a random access preamble. When a
channel request is received from the wireless device at an access
node, the access node can provide a positive indication that access
is permitted in a random access response. There exist a limited
number of contention-based preambles, and multiple wireless devices
transmitting the same preamble may result in a "collision" due to
interference between the two identical preambles. As a result, only
one of the wireless devices receives a positive indication in the
random access response, while the other wireless device needs to
re-initiate the contention-based random access procedure.
OVERVIEW
Exemplary embodiments described herein include systems, methods,
and processing nodes for contention-based random access. A method
for contention-based random access includes determining a
retransmission power and a backoff window for a retransmission of a
connection request to an access node from at least one of two or
more wireless devices, comparing a scaled product of the
retransmission power and backoff window with a predefined
retransmission success rate, and upon determining that the scaled
product is not substantially equal to the predefined retransmission
success rate, adjusting the retransmission power and backoff window
prior to transmitting the retransmission power and backoff window
to the at least one of said two or more wireless devices.
A system for contention-based random access includes an access node
for providing network services to one or more wireless devices, and
a processor communicatively coupled to the access node. The
processor configures the access node to perform operations
including obtaining a location and a quality of service (QoS) of a
wireless device that lost a contention-based random access
procedure and, based on the location, the QoS, and a cell load of
the access node, determining a retransmission power and a backoff
parameter for the wireless device. A scaled product of the
retransmission power and the backoff parameter represents a success
rate for a subsequent preamble transmitted by the wireless device.
Upon determining that the scaled product meets a threshold success
rate, the retransmission power and the backoff parameter are
transmitted to the wireless device.
A processing node for contention-based random access includes a
processor for enabling the processing to perform operations
including determining a retransmission power and a backoff window
for a preamble transmitted by a wireless device to an access node,
scaling the backoff window based on a cell load of the access node,
and comparing a product of the retransmission power and the scaled
backoff window with a predefined threshold. The predefined
threshold represents a probability of success of the preamble
reaching the access node.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 depicts an exemplary system for contention-based random
access.
FIG. 2 depicts an exemplary access node for performing
contention-based random access operations.
FIG. 3 depicts an exemplary method for contention-based random
access.
FIGS. 4A-4C depict graphs of exemplary retransmission parameters
for a contention-based random access request.
FIG. 5 depicts an exemplary processing node.
DETAILED DESCRIPTION
In embodiments disclosed herein, retransmission parameters are
determined for and transmitted to a wireless device based on a
desired retransmission success rate, or probability of success. The
retransmission success rate reflects a probability that subsequent
random access requests transmitted from the wireless device
re-initiating a contention-based random access procedure with an
access node will reach the access node. The retransmission
parameters are determined based on at least a quality of service
(QoS) associated with the wireless device, a distance of the
wireless device from the access node, and a cell load of the access
node. The QoS of the wireless device is used to determine the
desired retransmission success rate. The retransmission parameters
include a retransmission power level (or simply, "power") and a
retransmission backoff window size (or simply, "backoff window").
The power is generally an increased power level used for the
retransmission of the random access request, and the backoff window
is a time period after which the wireless device re-initiates the
retransmission. The power may be determined based on the distance
of the wireless device from the access node, and the backoff window
may be determined based on a congestion level or cell load of the
random access channel deployed by the access node. Further, a
product of the power and backoff window is scaled such that it can
be equated with the retransmission success rate or probability of
success. The parameters are adjusted to meet the desired
retransmission success rate, while remaining below maximum
constraints for the access node. These and additional operations
are further described with respect to the embodiments depicted in
FIGS. 1-5 below.
FIG. 1 depicts an exemplary system 100 for contention-based random
access. System 100 comprises a communication network 101, gateway
102, controller node 104, access node 110, and wireless devices
120, 130. Access node 110 is illustrated as having coverage area
112. Wireless devices 120, 130 are located within coverage area
112, and are in wireless communication with access node 110 via
communication links 121, 131, respectively. In exemplary
embodiments described herein, access node 110 determines a
contention between identical random access preambles transmitted
from each of wireless devices 120, 130, determines retransmission
parameters for one of wireless devices 120, 130 that lost the
contention, and transmits the retransmission parameters to said one
of wireless devices 120, 130. The retransmission parameters are
determined based on a distance of said one of wireless devices 120,
130 from access node 110, and a congestion of a random access
channel deployed by access node 110, such as a physical random
access channel (PRACH). Further, the retransmission parameters are
adjusted such that a scaled product of the retransmission
parameters satisfies a desired minimum retransmission success rate
based on a QoS of said one of wireless devices 120, 130. For
example, a connection requiring a high QoS, such as a voice call,
may be assigned higher power and/or larger backoff window
parameters, which are bounded by its packet delay budget defined by
the QoS. The bounding condition is necessary because a longer
backoff window size causes larger latency as well which may violate
the packet delay budget defined by the QoS assigned to said one of
wireless devices 120. Increasing the backoff window size works only
if the maximum backoff windows is still bounded by the packet delay
budget. Consequently, the scaled product of the parameters is
larger, thereby increasing the probability of success of subsequent
connection requests. In other words, when said one of wireless
devices 120, 130 re-initiates a contention-based random access
procedure, it is more likely that the retransmitted preamble is
heard by access node 110.
Wireless devices 120, 130 may be any device, system, combination of
devices, or other such communication platform capable of
communicating wirelessly with access node 110 using one or more
frequency bands deployed by access node 110. Wireless devices 120,
130 may be, for example, a mobile phone, a wireless phone, a
wireless modem, a personal digital assistant (PDA), a voice over
internet protocol (VoIP) phone, a voice over packet (VOP) phone, or
a soft phone, as well as other types of devices or systems that can
exchange audio or data via access node 110. Other types of
communication platforms are possible.
Communication network 101 can be a wired and/or wireless
communication network, and can comprise processing nodes, routers,
gateways, and physical and/or wireless data links for carrying data
among various network elements, including combinations thereof, and
can include a local area network a wide area network, and an
internetwork (including the Internet). Communication network 101
can be capable of carrying data, for example, to support voice,
push-to-talk, broadcast video, and data communications by wireless
devices 120, 130, etc. Wireless network protocols can comprise
MBMS, code division multiple access (CDMA) 1xRTT, Global System for
Mobile communications (GSM), Universal Mobile Telecommunications
System (UMTS), High-Speed Packet Access (HSPA), Evolution Data
Optimized (EV-DO), EV-DO rev. A, Third Generation Partnership
Project Long Term Evolution (3GPP LTE), and Worldwide
Interoperability for Microwave Access (WiMAX). Wired network
protocols that may be utilized by communication network 101
comprise Ethernet, Fast Ethernet, Gigabit Ethernet, Local Talk
(such as Carrier Sense Multiple Access with Collision Avoidance),
Token Ring, Fiber Distributed Data Interface (FDDI), and
Asynchronous Transfer Mode (ATM). Communication network 101 can
also comprise additional base stations, controller nodes, telephony
switches, internet routers, network gateways, computer systems,
communication links, or some other type of communication equipment,
and combinations thereof.
Communication links 106, 107 can use various communication media,
such as air, space, metal, optical fiber, or some other signal
propagation path--including combinations thereof. Communication
links 106, 107 can be wired or wireless and use various
communication protocols such as Internet, Internet protocol (IP),
local-area network (LAN), optical networking, hybrid fiber coax
(HFC), telephony, T1, or some other communication format--including
combinations, improvements, or variations thereof. Wireless
communication links can be a radio frequency, microwave, infrared,
or other similar signal, and can use a suitable communication
protocol, for example, Global System for Mobile telecommunications
(GSM), Code Division Multiple Access (CDMA), Worldwide
Interoperability for Microwave Access (WiMAX), or Long Term
Evolution (LTE), or combinations thereof. Communications links 106,
107, 108, 109 may include S1 communications links. Other wireless
protocols can also be used. Communication links 106, 107 can be a
direct link or might include various equipment, intermediate
components, systems, and networks. Communication links 106, 107 may
comprise many different signals sharing the same link
Gateway node 102 can be any network node configured to interface
with other network nodes using various protocols. Gateway node 102
can communicate user data over system 100. Gateway node 102 can be
a standalone computing device, computing system, or network
component, and can be accessible, for example, by a wired or
wireless connection, or through an indirect connection such as
through a computer network or communication network. For example,
gateway node 102 can include a serving gateway (SGW) and/or a
public data network gateway (PGW), etc. One of ordinary skill in
the art would recognize that gateway node 102 is not limited to any
specific technology architecture, such as Long Term Evolution (LTE)
and can be used with any network architecture and/or protocol.
Gateway node 102 can comprise a processor and associated circuitry
to execute or direct the execution of computer-readable
instructions to obtain information. Gateway node 102 can retrieve
and execute software from storage, which can include a disk drive,
a flash drive, memory circuitry, or some other memory device, and
which can be local or remotely accessible. The software comprises
computer programs, firmware, or some other form of machine-readable
instructions, and may include an operating system, utilities,
drivers, network interfaces, applications, or some other type of
software, including combinations thereof. Gateway node 102 can
receive instructions and other input at a user interface.
Controller node 104 can be any network node configured to
communicate information and/or control information over system 100.
Controller node 104 can be configured to transmit control
information associated with a handover procedure. Controller node
104 can be a standalone computing device, computing system, or
network component, and can be accessible, for example, by a wired
or wireless connection, or through an indirect connection such as
through a computer network or communication network. For example,
controller node 104 can include a mobility management entity (MME),
a Home Subscriber Server (HSS), a Policy Control and Charging Rules
Function (PCRF), an authentication, authorization, and accounting
(AAA) node, a rights management server (RMS), a subscriber
provisioning server (SPS), a policy server, etc. One of ordinary
skill in the art would recognize that controller node 104 is not
limited to any specific technology architecture, such as Long Term
Evolution (LTE) and can be used with any network architecture
and/or protocol.
Controller node 104 can comprise a processor and associated
circuitry to execute or direct the execution of computer-readable
instructions to obtain information. Controller node 104 can
retrieve and execute software from storage, which can include a
disk drive, a flash drive, memory circuitry, or some other memory
device, and which can be local or remotely accessible. In an
exemplary embodiment, controller node 104 includes a database 105
for storing information such as relationships between QoS/priority
classes and predefined retransmission success rates for each of
wireless devices 120, 130. The software comprises computer
programs, firmware, or some other form of machine-readable
instructions, and may include an operating system, utilities,
drivers, network interfaces, applications, or some other type of
software, and combinations thereof. Controller node 104 can receive
instructions and other input at a user interface.
Access node 110 can be any network node configured to provide
communication between wireless devices 120, 130, and communication
network 101. Access node 110 can be a standard access node and/or a
short range, low power, small access node. A standard access node
can be a macrocell access node such as a base transceiver station,
a radio base station, an eNodeB device, or an enhanced eNodeB
device, or the like. In an exemplary embodiment, a macrocell access
node can have a coverage area 112 in the range of approximately
five kilometers to thirty five kilometers and an output power in
the tens of watts. A small access node can include a microcell
access node, a picocell access node, a femtocell access node, or
the like such as a home NodeB or a home eNodeB device. Moreover, it
is noted that while access node 110 is illustrated in FIG. 1, any
number of access nodes can be implemented within system 100.
As depicted in further detail in FIG. 2, access node 110 can
comprise a processor and associated circuitry to execute or direct
the execution of computer-readable instructions to obtain
information. Access node 110 can retrieve and execute software from
storage, which can include a disk drive, a flash drive, memory
circuitry, or some other memory device, and which can be local or
remotely accessible. The software comprises computer programs,
firmware, or some other form of machine-readable instructions, and
may include an operating system, utilities, drivers, network
interfaces, applications, or some other type of software, including
combinations thereof. Access node 110 can receive instructions and
other input at a user interface. Access node 110 communicates with
gateway node 102 and controller node 104 via communication links
106, 107.
Other network elements may be present in system 100 to facilitate
communication but are omitted for clarity, such as base stations,
base station controllers, mobile switching centers, dispatch
application processors, and location registers such as a home
location register or visitor location register. Furthermore, other
network elements that are omitted for clarity may be present to
facilitate communication, such as additional processing nodes,
routers, gateways, and physical and/or wireless data links for
carrying data among the various network elements, e.g. between
access node 110 and communication network 101.
FIG. 2 depicts an exemplary access node for performing
contention-based random access operations. In this embodiment,
access node 210 is a macro-cell access node (or "macro") as
described above. In other embodiments, access node 210 can be any
other type of access node including a small-cell access node, such
as a relay node. In this embodiment, macro 210 is configured as an
access point for providing network services from network 201
directly to end-user wireless devices 220. 230. Macro 210 is
illustrated as comprising a memory 211 for storing logical modules
including modules for performing operations described herein (for
example, as shown in FIG. 3), a processor 212 for executing the
logical modules, a transceiver 213, and an antenna 214 for
communication with one or more wireless devices, including wireless
devices 220, 230 via communication links 221, 231 respectively.
Further, macro 210 is communicatively coupled to network 201 via
communication interface 206, which may include additional
components connected via any wired or wireless link as described
above. For instance, there may be gateways and/or controllers in a
path of communication interface 206. If access node 210 is a relay,
then there may be additional access nodes in path 206. Moreover,
although only one transceiver and antenna combination is depicted
in access node 210, additional transceivers and antennas may be
incorporated in order to deploy multiple frequency bands and to
facilitate communication across other network nodes that are not
shown, such as gateways, controllers, and other access nodes. In
embodiments described herein, macro 210 deploys a random access
channel or cell, such as a PRACH, whereby congestion of the channel
is used as a factor among others in determining retransmission
parameters for a wireless device that lost a contention.
FIG. 3 depicts an exemplary method for contention-based random
access. The method is discussed with reference to the exemplary
access node 210 illustrated in FIG. 2. However, the method can be
implemented with any suitable network node. In addition, although
FIG. 2 depicts steps performed in a particular order for purposes
of illustration and discussion, the methods discussed herein are
not limited to any particular order or arrangement. One skilled in
the art, using the disclosures provided herein, will appreciate
that various steps of the methods can be omitted, rearranged,
combined, and/or adapted in various ways.
The method begins with a detection of a contention. For example,
two wireless devices attempt to initiate a random access procedure
to connect to the access node by transmitting the same preamble
over the PRACH at the same time. In this case, the two preambles
may interfere with each other and the access node receives neither
preamble, such that neither wireless device receives any response
(HARQ ACK) from the access node, and both wireless devices
determine that the procedure has failed. Alternatively, the access
node could successfully decode the preamble from only one wireless
device, and fail to decode the preamble from the other wireless
device, in which case the wireless device with the successful
message will receive the HARQ ACK from the access node, i.e. a
"contention resolution", whereas the other wireless device has
"lost" the contention, and has to retransmit the preamble. Thus,
the remaining operations are performed to determine optimal
retransmission parameters for the wireless device that lost the
contention.
At 301, a distance is obtained between said wireless device that
lost the contention (hereinafter referred to as "the wireless
device" for the purposes of this embodiment), and the access node.
A QoS of the wireless device is obtained. A target probability of
success is determined based on the QoS. The target probability of
success or, in other words, a desired retransmission success rate,
indicates a probability that subsequently transmitted random access
requests will reach the access node. Moreover, the QoS may include
a packet delay budget for the wireless device. Thus, the target
probability of success is based on the packet delay budget. For
example, different applications of the wireless device may have
different packet delay budgets. An emergency call may have a low
delay budget, thereby requiring a higher probability of success for
subsequent retransmissions. Associations between different QoS
levels and corresponding desired success rates may be stored on the
access node, or on a separate node such as a controller node, which
may be queried by the access node.
At 302, retransmission parameters including a retransmission power
and a backoff window are determined based on the distance of the
wireless device from the access node and on a cell load of the
access node. For example, if the wireless device does not receive a
random access response (RAR) after the previous preamble
transmission, it is supposed to re-initiate the random access
procedure. In other cases, the wireless device may receive a RAR
from the access node, but the preamble index in the RAR is not
intended for the wireless device, and may be intended for another
wireless device, i.e. the wireless device that successfully
transmitted the original preamble. In this case, a backoff
indicator value (or "backoff window") is transmitted with the RAR
to control the retransmission timing.
The retransmission power is a power level used for the
retransmission of the random access request, usually measured in
decibels (dB). The wireless device can retransmit the preamble with
the same power level as the previous preamble, or may try using a
higher power level. Thus, the retransmission power provides the
wireless device with a maximum or incremental increase amount in
the power level to be used for retransmission. For instance, the
retransmission power can be provided to the wireless device (at the
end of the method) in a powerRampingStep portion of a SIB2 message.
Further, the retransmission power is determined based on the
distance of the wireless device from the access node. For example,
a first wireless device close to base station will transmit at
lower power level as compared with a second wireless device at an
edge of a coverage area, to ensure that the retransmitted preamble
reaches the access node.
The retransmission backoff window size (or "backoff window") is a
time period after which the wireless device re-initiates the
retransmission. In other words, the backoff window indicates a time
delay between the previous transmission and the next transmission.
In some embodiments, the backoff window is provided as a backoff
indicator (BI) parameter within a special MAC subheader. In this
case, the BI parameter comprises 4 bits, carrying a value from
0-15, with each value being mapped to a specific time window. For
more details please refer to 3GPP technical specification 36.321.
Further, the backoff window may be determined based on a congestion
level or cell load of the random access channel (e.g. PRACH)
deployed by the access node. For instance, if the PRACH is heavily
loaded, then a high backoff window is required to avoid additional
preamble collisions. If the PRACH is lightly loaded, then a
moderate to low back off window may be sufficient to avoid
collisions. The maximum backoff window size could be also related
with the packet delay budget defined by QoS. For example, the
maximum backoff window size of a random access procedure initiated
for a voice packet should be smaller than the maximum backoff
window size of a random access procedure initiated for a best
effort packet. Moreover, the power and backoff window are
determined such that a scaled product of the power and backoff
window meets a desired retransmission success rate. FIGS. 4A-4C
show the scaled product in further detail. Generally, the backoff
window may be adjusted by a scaling factor, thus the scaled product
may include a product of the retransmission power and the scaled
backoff window. Other methods of determining a scaled product may
be apparent to those having ordinary skill in the art in light of
this disclosure. In other words, step 302 defines a function for
determining the power and backoff window appropriate for a QoS of
the wireless device using the distance from the access node and a
scaling factor associated with the cell load.
At 303, the retransmission parameters (i.e. power and backoff
window) are compared with constraints for the access node. The
constraints may be defined based on the cell load of the access
node, or other characteristics of the access node. For instance, as
shown in FIGS. 4B-4C, maximum constraints on the power level and
the backoff window may be defined, and the parameters adjusted to
meet both the maximum constraints and the desired success rate. The
parameters may therefore be adjusted at 304, prior to being
transmitted to the wireless device. For instance, the
retransmission power can be provided to the wireless device in a
powerRampingStep portion of a SIB2 message, and the backoff window
may be provided as a backoff indicator (BI) parameter within a
special MAC subheader.
FIGS. 4A-4C depict graphs of exemplary retransmission parameters
for a contention-based random access request. As described herein,
operations are performed that target a desired random access
probability of success based on the QoS of the wireless device. The
vertical axis 401 represents the retransmission power and the
horizontal axis 402 represents the backoff window size/time. The
backoff window size may be scaled by a scaling factor based on the
current PRACH cell load. A two-dimensional area calculation of a
selected power level 401 and backoff window size 402 may be equated
with a particular success rate. For example, with reference to FIG.
4A, scaled product 406 comprises a selected power level and backoff
window size that equates to a 100% probability of success. In an
embodiment, scaled product 406 may comprise a product of a maximum
allowable power level and backoff window size for a particular
congestion level of an access node. Further, scaled product 405
comprises a product of a power level and backoff window size that
equates to a 50% probability of success. Generally, depending on
the QoS of the wireless device, any desired probability of success
between 50% and 100% may be defined, and parameters adjusted
accordingly. It should be noted that the scaled product does not
linearly correspond to the probability of success, but instead is
an approximation of the probability of success. Consequently,
various scaling factors and product calculations may be used, so
long as they generally represent a probability of success for
retransmissions from the wireless device.
Moreover, the product may be not necessarily be represented as a
square, as depicted in FIG. 4A. For instance, referring to FIGS. 4B
and 4C, either the power level or the backoff window size may be
adjusted to satisfy a maximum threshold, so long as the area of the
two-dimensional depiction is approximately equivalent to the
desired probability of success. With reference to FIG. 4B, scaled
products 405 and 410 correspond to the same retransmission success
rate. However, scaled product 410 comprises a power level that is
increased until it reaches a maximum power level 420, upon which it
cannot go any higher. Such parameter selection may be useful, for
instance, for a wireless device that is a long distance away from
the access node, thereby requiring a higher power level 401 for
retransmission, and is able to use a smaller backoff window size
402 while maintaining a desired success rate. In this case, the
maximum power level 420 may be defined based on, for instance, a
cell load of the PRACH channel. Further with reference to FIG. 4C,
scaled products 405 and 411 correspond to the same retransmission
success rate. However, scaled product 411 comprises a backoff
window size that is increased until it reaches a maximum backoff
window size 421, upon which it cannot take any longer. The power
level 401 is correspondingly lowered so as to maintain the desired
level of success without using excessive power. Such parameter
selection may be useful, for instance, for a wireless device that
is relatively close to access node, but where the PRACH channel is
congested, thereby requiring a larger backoff window size while
maintaining a desired success rate. The maximum backoff window size
421 may be defined based on, for instance, a cell load of the PRACH
channel, as well as the packet delay budget defined by QoS.
Generally, any combination of power and back-off window size may be
determined subject to constraints 420, 421, so long as the scaled
product is equivalent to the desired retransmission success
rate.
The methods, systems, devices, networks, access nodes, and
equipment described above may be implemented with, contain, or be
executed by one or more computer systems and/or processing nodes.
The methods described above may also be stored on a non-transitory
computer readable medium. Many of the elements of communication
system 100 may be, comprise, or include computers systems and/or
processing nodes. This includes, but is not limited to: access
nodes 110, 210, wireless devices 120, 130, and/or network 101.
FIG. 5 depicts an exemplary processing node 500 comprising
communication interface 502, user interface 504, and processing
system 506 in communication with communication interface 502 and
user interface 504. Processing system 506 includes storage 508,
which can comprise a disk drive, flash drive, memory circuitry, or
other memory device. Storage 508 can store software 510 which is
used in the operation of the processing node 500. Storage 508 may
include a disk drive, flash drive, data storage circuitry, or some
other memory apparatus. For example, storage 508 may include a
buffer. Software 510 may include computer programs, firmware, or
some other form of machine-readable instructions, including an
operating system, utilities, drivers, network interfaces,
applications, or some other type of software. For example, software
510 may include a retransmission parameter determination module.
Processing system 506 may include a microprocessor and other
circuitry to retrieve and execute software 510 from storage 508.
Processing node 500 may further include other components such as a
power management unit, a control interface unit, etc., which are
omitted for clarity. Communication interface 502 permits processing
node 500 to communicate with other network elements. User interface
504 permits the configuration and control of the operation of
processing node 500.
The exemplary systems and methods described herein can be performed
under the control of a processing system executing
computer-readable codes embodied on a computer-readable recording
medium or communication signals transmitted through a transitory
medium. The computer-readable recording medium is any data storage
device that can store data readable by a processing system, and
includes both volatile and nonvolatile media, removable and
non-removable media, and contemplates media readable by a database,
a computer, and various other network devices.
Examples of the computer-readable recording medium include, but are
not limited to, read-only memory (ROM), random-access memory (RAM),
erasable electrically programmable ROM (EEPROM), flash memory or
other memory technology, holographic media or other optical disc
storage, magnetic storage including magnetic tape and magnetic
disk, and solid state storage devices. The computer-readable
recording medium can also be distributed over network-coupled
computer systems so that the computer-readable code is stored and
executed in a distributed fashion. The communication signals
transmitted through a transitory medium may include, for example,
modulated signals transmitted through wired or wireless
transmission paths.
The above description and associated figures teach the best mode of
the invention. The following claims specify the scope of the
invention. Note that some aspects of the best mode may not fall
within the scope of the invention as specified by the claims. Those
skilled in the art will appreciate that the features described
above can be combined in various ways to form multiple variations
of the invention. As a result, the invention is not limited to the
specific embodiments described above, but only by the following
claims and their equivalents.
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